-[-5 Memoirs of the Indian Museum. [Vol III, 



The two varieties were taken together in a trawl on December 6th, iqoq, in 

 brackish water in the Satterniukhi River, Ganges delta. 



Genus Tropidichthys, Bleeker. 



Key to the Indian species of Tropidichthys. 



A.— A large black ocellus present at the base of the 

 dorsal fin. 

 [a] Pale ocelU on the snout, sides and caudal fin . . T. mar gar Hat us. 

 [a') Pale ocelli absent from the caudal fin .. T. bennettii. 



B. — No dark ocellus at the base of the dorsal fin. 



[h) Dark markings consisting solely of delicate 



longitudinal and transverse lines ; no pale ocelli T. investigator is. 

 {/>') Somewhat irregular dark bands present; sides 



with pale ocelli . . . . . . T. valentini. 



Bieeker in 1854 referred those species with ridged back and inconspicuous nasal 

 organs to a genus Tropidichthys. In 1865 he called the species with these characters 

 Psilonotus. Giinther regarded them as a subgenus of Tetrodon under the name of 

 Anosmius, Peters, 1855 ; and Day treated them as a division of Tetrodon. 



Tropidichthys margaritatus , Riipp. 



(Plate i, fig. 3.) 



There are four specimens in the Museum, all taken by the " Golden Crown" off 

 the Madras coast. The lines under the eye are nearly horizontal, and not radiating. 

 There are no horizontal lines on the lower part of the head, and the small ocelli on 

 the tail show a tendency to run together and form ventral bars. Those on the ventral 

 surface are very faint, if they can be distinguished at all. 



Tropidichthys investigator is, .sp. nov. 



(Platei, fig. 4.) 



Two specimens from the Andamans (St. 239 of the "Investigator") at a depth 

 of 55 fathoms. 



D. g-io. P. 15. A. 10. C. II. 



Outline of back distinctly angular, the highest point being ju.st above the gill- 

 opening. Depth of body very variable. The whole of head and body, except the 

 tail, covered with small spines which lie parallel to the skin. Each spine with two 

 roots. 



No dark spot at base of dorsal fin Fins practically colourless. Back and 

 sides pale brown. Three narrow somewhat sinuous dark lines crossing the snout 

 in front of the eye, the two posterior ones bending inwards towards the orbit; a 

 fourth Hne joining the orbits near the centre; at lea.st one similar line across the 



